Skeletal muscle contractility is defined as the capability of the contractile proteins in a muscle to interact and generate force. All body movement are dependent on contractions of skeletal muscles. Consequently, any decline in skeletal muscle contractility results in some degree of immobility. Contractility is impaired by many muscle disease, random and engineered genetic mutations, and even healthy aging. Quantitative knowledge of the contractility of skeletal muscles of skeletal muscles is necessary to test hypotheses regarding the interactions between deficits in basic cellular and molecular processes and musculoskeletal frailty and immobility. Briefly, the specific aims of the Contractility Core are to provide for NSC investigators: (1) facilities, expertise, and technical support for measuring contractility of whole skeletal muscles and small strips of intact fibers from the diaphragm muscle (2) instruction and training in the knowledge and skills necessary to measure contractility; and (3) development of techniques and/or construction of specialized apparatus for the study of the contractility. Contractility is measured initially at the level of the whole skeletal muscle to provide the broadest spectrum of functional changes arising from cellular and molecular changes in skeletal muscle fibers due to aging or experimental interventions. At later stages in a project, more sophisticated evaluations may be required at the cellular or molecular levels. The Contractility Core was developed to ensure that all NSC investigators are able to include valid and reliable measurements of skeletal muscle contractility in their experiments. Consequently, the Contractility Core provides reliable measurements of skeletal muscle contractility in their experiments. Consequently, the Contractility Core provides free to a NSC investigators: (1) one study of six pairs of control and experimental rodents; (2) assistance in education and training NSC investigators, their staff, or their trainees to set-up the apparatus and measure contractility independently; and (3) assistance in the development of one innovative technique, or the construction of one specialized instrument for the measurement of contractility per year. Subsequent use of the Core is generally on a fee-for-service basis, but if results are promising and particularly if the NSC investigator proposes to seek outside funding, additional experiments may be supported by the Core budget from unallocated charge-back-fees. Through the provision of state-of-the-art facilities, techniques and expertise, the Core enhances and encourages multi-disciplinary research in the basic biology of aging at UM and Worldwide. The significance of the Contractility Core to NSC investigators is evidenced by the increase in the number of users from the seven UM scientists in 1995 to nineteen UM and fourteen external scientists in 1999.